path: root/Documentation/padata.txt
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authorColin Cross <ccross@android.com>2015-10-27 23:42:08 (GMT)
committerDenis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>2020-04-10 23:05:20 (GMT)
commitd331fe22ba50ab425a0c7e6903b61a0c4587508d (patch)
tree729c8b02a46370bf5bb63ae25963041dd52cf47a /Documentation/padata.txt
parent57d294a5148db072f7e15d4c2a8603417b4291b5 (diff)
ANDROID: mm: add a field to store names for private anonymous memoryHEADreplicant-9
Userspace processes often have multiple allocators that each do anonymous mmaps to get memory. When examining memory usage of individual processes or systems as a whole, it is useful to be able to break down the various heaps that were allocated by each layer and examine their size, RSS, and physical memory usage. This patch adds a user pointer to the shared union in vm_area_struct that points to a null terminated string inside the user process containing a name for the vma. vmas that point to the same address will be merged, but vmas that point to equivalent strings at different addresses will not be merged. Userspace can set the name for a region of memory by calling prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, start, len, (unsigned long)name); Setting the name to NULL clears it. The names of named anonymous vmas are shown in /proc/pid/maps as [anon:<name>] and in /proc/pid/smaps in a new "Name" field that is only present for named vmas. If the userspace pointer is no longer valid all or part of the name will be replaced with "<fault>". The idea to store a userspace pointer to reduce the complexity within mm (at the expense of the complexity of reading /proc/pid/mem) came from Dave Hansen. This results in no runtime overhead in the mm subsystem other than comparing the anon_name pointers when considering vma merging. The pointer is stored in a union with fieds that are only used on file-backed mappings, so it does not increase memory usage. Includes fix from Jed Davis <jld@mozilla.com> for typo in prctl_set_vma_anon_name, which could attempt to set the name across two vmas at the same time due to a typo, which might corrupt the vma list. Fix it to use tmp instead of end to limit the name setting to a single vma at a time. Bug: 120441514 Change-Id: I9aa7b6b5ef536cd780599ba4e2fba8ceebe8b59f Signed-off-by: Dmitry Shmidt <dimitrysh@google.com> [AmitP: Fix get_user_pages_remote() call to align with upstream commit 5b56d49fc31d ("mm: add locked parameter to get_user_pages_remote()")] Signed-off-by: Amit Pundir <amit.pundir@linaro.org> Rebased for 5.3 kernel Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
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